writing a method to calculate income tax. Variable not initializing

I am writing a method to calculate income tax based on gross pay and number of dependents. When I try and compile the following code, my dTaxOnIncome variable is getting not initialized.

    public static double incomeTax(double gross, int dependents)
{
            double dTaxOnIncome;                // holds the calculated income tax.

            if(gross >= 10000 && dependents == 0)
            {
                dTaxOnIncome = gross * .25; 
            }
            else
            {   
                if((gross >= 10000) && ((dependents >= 1 && dependents <= 4)))
                {
                    if(dependents == 1)
                    {
                        dTaxOnIncome = gross * .24;
                    }
                    else
                    {
                        if(dependents == 2)
                        {   
                            dTaxOnIncome = gross * .23; 
                        }
                        else
                        {
                            if(dependents == 3)
                            {
                                dTaxOnIncome = gross * .22; 
                            }
                            else
                            {
                                if(dependents == 4)
                                {
                                    dTaxOnIncome = gross * .21; 
                                }
                                else 
                                {   
                                    if(dependents == 5)
                                    {
                                        dTaxOnIncome = gross * .205; 
                                    }
                                    else
                                    {
                                        if(dependents == 6)
                                        {
                                            dTaxOnIncome = gross * .20; 
                                        }
                                        else 
                                        {
                                            if(dependents > 6)
                                            {
                                                dTaxOnIncome = gross * .18;
                                            }
                                            else
                                            {   
                                            }   

                                        }
                                    }
                                }
                            }   
                        }
                    }
                }
            }
    return dTaxOnIncome;    
}// end incomeTax (double, int) 

I know that I could use if else statements, but I have tried this problem multiple ways and this seemed to be the most straight forward.